Bonded abrasive articles containing fillers



Patented Jan. 19, 1943 BONDED ABRASIVE ARTICLES CONTAINING FILLERS Samuel S. Kistler, West Boylston, Mass, assignor to Norton Company, Worcester, Mass, at corporation of Massachusetts No Drawing. Application April 15, 1942, Serial No. 439,125

7 Claims.

ditions of use to cryolite which heretofore has been considered the best all round filler for certain types of abrasive producta'Another object of the invention is to find a filler which gives a higher quality number Q where where K is a constant, M is material removed and W is wheel wear. Another object of the invention is to find a filler which gives a higher ratio of material removed to wheel wear. Other objects will be in part obvious or in part pointed out hereinafter. Efliciency of grinding wheels has in the pa been stated in terms of ratio of material removed to wheel wear. This quite accurately gives the economy of grinding so far as the cost of abrasive is concerned, if like quantities of abrasive are assumed to cost like' amounts. But let us assume two wheels having the same ratio in a given grinding job but where the material removed by wheel A in a given time is twice that M2 wmeasures the economy of grinding wheels in many grinding operations providing a large allowance for labor cost and also for overhead.

Nevertheless in some dry snagging operations the true economy is an expression 2M W I where n is a number between 1 and 2. In the formula the constant K is used simply to make the figures approximate some figures derived from earlier formulae and so, for relative results it can be ignored. It follows that in a comparison of fillers in otherwise identical grinding wheels grinding under the same conditions, one which gives a, higher Q number where and which also has a higher ratio where r ti a ois a superior filler for many snagging operations.

In accordance with my invention, I have found that the quality and economy of abrasive articles, and particularly grinding wheels, may be materially improved by incorporating therein a fluoborate of an alkali metal (including ammonium fluoborate), and particularly sodium fluoborate or potassium fluoborate. These salts are particularly useful as fillers in different types of grinding wheels when the latter are used in dry grinding operations. Potassium fluoborate is the preferred agent because it is substantially insoluble and it has a low melting point of 530 C. Also, it does not react with the bond during normal periods of rest. The low solubility characteristic is important because of the fact that if a trace of filler is left on the work it cannot form a soluble salt deposit which at some later time would tend to corrode the metal..

It has been found that cryolite has a quality number about four times that of kaolin when used as a filler in a resinoid bonded grinding wheel. I have found that the alkali metal fluoborates are superior to cryolite in improving the quality of various types of abrasive articles as shown by both the quality number and the ratio. For example, two grinding wheels were made of the same type oi. bond and grade and structure characteristics except that one contained cryolite and the other the same proportion of potassium fluoborate. Each wheel was made of the same type and size of abrasive grains bonded by a similar phenol formaldehyde bond and the materials were proportioned to provide a W grade of hardness on the Norton scale and a structure having by volume of abrasive and 8% of pores. That wheel having potassium fluoborate as a filler gavea quality number which was 56% higher than that of the cryolite filled wheel. Another test with similar wheels showed that the potassium fluoborate had 33% higher quality number than the other. In another test, two

wheels were made with the same phenol formaldehyde resin bond and the ingredients were proportioned to provide a grade of S and a structure having 58% 01' abrasive and 16% of pores. Each wheel contained 4% by volume of calcium oxide and 21% of filler, one filler being cryolite and the other being potassium fluoborate. The wheel filled with the fluoborate had a nuality number 24% higher than that of the cryolite filled wheel.

In another test with wheels having abrasive grains of number 12 grit size bonded by a phenol formaldehyde resinoid to a grade of W on the Norton scale, and a structure having 60% by volume of abrasive and 8% of pores, the operation involved grinding stainless steel with a swing frame grinder having a load of 125 lbs. on the swing frame. The wheels were similar except that one wheel contained cryolite and the other contained an equal amount of potassium fluoborate, and the grinding results were as follows:

Wheel W881 1nWhcubic es per Material removed M pounds per hour Ratio R Filler M This, in connection with the other data indicates that potassium fluoborate is superior to cryolite in many grinding operations, and in every case which I investigated and by every criterion this was found to be so.

As one example of carrying out the invention, I may proceed as follows: I provide a quantity of abrasive, such as fused alumina or silicon carbide, place it in a mixing pan, and wet it with furfural. I add a quantity of dry A" stage phenol formaldehyde resin containing a suitable hardening agent, such as hexamethylene tetramine, and preferably also containing a small quantity of calcium oxide CaO as a dehydrating agent and further containing alkali metal fluoborate in any amount within the above limits. Mixing is continued and then a wheel is molded and cured in any known manner. That is, it may be hot pressed or it may be cold pressed and then baked in an oven. In a typical example of the foregoing, the alkali metal fiuoborate was 21% of the bond by volume.

Another type of grinding wheel may be made of abrasive grains united by an organic resinoid bond containing aniline formaldehyde as its primary constituent. Such a wheel may be made, for example, of abrasive grains and bond proportioned to provide a structure of 54% abrasive grains and 0% of pores. The grains may be first'wet or plasticized" with furfural and then a mixture of aniline formaldehyde resin powder, and potassium fluoborate may be mixed with the grains. Such a mixture may be molded and hot pressed to form a grinding wheel. Other fillers, dehydrating agents, etc. may also be incorporated in the bond mass, if desired.

This active filler of the present invention may also be incorporated in a rubber bonded grinding wheel made by any usual or desired process.

A vitrified grinding wheel may have the filler incorporated therein by the following procedure. The bonded abrasive grinding wheel may be first made in accordance with standard practice to provide a given grade and percentage of porosity. The pores in the wheel form interconnected passages open at the surface of the wheel. These pores are thereafter impregnated with a mass comprising the alkali metal fluoborate suspended in a supplemental fluid bond, such as a. standard "Bakelite type of phenol formaldehyde condensation product "in the liquid and incompletely converted state. The suspension of potassium fiuoborate in the fiuidresinoid may be forced into the wheel pores by suitable procedure. For example, the wheel may be placed in a vessel containing the filler suspended in the liquid bond and a vacuum may then be applied to draw the air out of the wheel and then when air is allowed to break the vacuum, the atmospheric pressure forces the liquid and the filler into the pores of the wheel. Thereafter, the wheel may be subjected to a further heating operation to convert the liquid resin to its final infusible state. This forms a supplemental bond within the wheel pores which holds the filler interspersed substantially uniformly throughout the pores of the wheel structure. Rubber in a fluid condition, such as a solution of rubber or rubber latex containing the potassium fiuoborate, may be used in place of the resin. Various other types of materials may be employed for carrying the filler and fixing it within the wheel pores.

The filler may be incorporated in the grinding wheel in any desired proportions. In general, the higher the content of filler, the better is the quality of the wheel, up to that limit at which the proportion of bond is lowered to a detrimental extent. The filler may usually constitute from about 5 to 60% or more by volume of the bond content employed and preferably from 10 to 35%. This proportion may be widely varied depending upon the grinding characteristics desired. Other types of fillers may also be incorporated in the bond for desired purposes, and the bonds may be widely varied within the knowledge of those skilled in the art.

Thus this invention involves the use of alkali metal fiuoborate as a filler or modifying agent in various types of bonded abrasive articles, wherein the filler changes or improves the quality or grinding characteristics thereof. It serves primarily to make a grinding wheel freer or cooler cutting or to remove more metal per unit of time for a given rate of wheel wear. Many modifications may be made in the composition of the abrasive article and in the methods of manufacture; hence the above disclosure is to be interpreted as illustrating the general principles of this invention and the preferred types and compositions of abrasive articles and not as limitations on the claims appended hereto.

I claim:

1. An abrasive article comprising abrasive grains, a bond uniting the grains as an integral body and alkali metal fiuoborate interspersed .hroughout the bonded mass.

2. An abrasive article comprising abrasive grains, an organic bond uniting the grains as an integral body and a filler of finely divided solid alkali metal fluoborate interspersed throughout the bond.

3. An abrasive article comprising abrasive grains and a resinoid bond which units the grains as an integral body, said bond having intimately associated therewith a filler comprising alkali metal fiuorborate which constitutes from 5 to 60% by weight of the bond mass.

4. An abrasive article comprising abrasive grains, 9. vulcanized rubber bond uniting the grains integrally and a filler containing from 5 to 60% of alkali metal fluoborate interspersed therethrough.

5. An abrasive article comprising abrasive grains, 9. vitrified ceramic bond uniting the grains as an integral body and proportioned to form interspersed pore spaces between the grains, and a supplemental bond and a filler comprising alkali metal fiuoborate in said pore spaces, said filler constituting from 5 to 60% by weight of the supplemental bond.

6. An abrasive article comprising abrasive grains, a bond uniting the grains as an integral body which has as its primary constituent a converted phenol formaldehyde condensation product, and a solid granular filler incorporated in the bond composed primarily of alkali metal fluoborate which constitutes from 5 to 60% of the bond mass, by volume.

'7. A grinding wheel comprising abrasive grains, a bond uniting the grains as an integral body which has as its primary constituent a heat converted phenol formaldehyde condensation prodnot, and solid potassium fiuoborate dispersed through the bond as a filler constituting from 10 to 35% by volume thereof.

SAMUEL s. 

